1. Field of the Invention
This invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile apparatus or a compound machine thereof in which an electrostatic latent image formed on an image bearing member on the basis of an electrophotographic process corresponding to a recorded image to be recorded is developed with a developer and is recorded on a transfer material or the like, and a method of controlling the image forming apparatus.
2. Related Background Art
An image forming apparatus adopting the electrophotographic process is generally designed such that a toner which is a charged developer is caused to adhere to an electrostatic latent image formed on the surface of an image bearing member to thereby form a toner image, and the toner image is transferred to transfer paper conveyed so as to contact with the image bearing member, and the transfer paper is subjected to a heat fixing process to thereby fix the toner image on the transfer paper, thus completing an image forming operation.
In this case, as the developer, use is generally made of a toner mixed with powder having magnetism which is called a carrier. Of the developer, the toner is charged in a developing apparatus so as to be attracted to the electrostatic latent image on the surface of the image bearing member.
Thus, when an image forming process is carried out, the toner in the developer is decreased. The image forming apparatus is usually provided with a developer toner density detecting portion for detecting the toner density of the developer. The developer toner density detecting portion, when the residual amount of toner in a developer container provided in the developing apparatus has become a predetermined amount or less, is adapted to detect that the residual amount of toner is small, so as to cause a toner supplying apparatus to perform a toner supplying operation by control means.
As described above, in the conventional image forming apparatus, it has been necessary to detect the toner density of the developer at a suitable time by the developer toner density detecting portion so that by automatic toner replenishment control means (ATR) for effecting appropriate toner replenishment in conformity with the fluctuation of the toner density, the toner density may always be kept within a predetermined allowable range relative to a predetermined reference value.
Now, the ATR is generally comprised of toner density detecting means for detecting the toner density of the developer, toner replenishment amount control means for processing the output data of this toner density detecting means and determining a toner replenishment amount, and toner supplying means for actually supplying the toner on the basis of the toner replenishment amount determined by this toner replenishment amount control means.
Particularly, various types of toner density detecting means have been put into practical use. The toner density detecting means include, for example, a toner density detecting device by an optical sensor utilizing the fact that the light reflectance of a developer in a developer container or on a developer bearing member is varied by the toner density, a toner density detecting device by a permeability sensor for converting the permeability of a developer into an electrical signal by utilizing the fact that the permeability of the developer is varied by the toner density, a toner density detecting device for detecting a variation in the light reflectance of a predetermined patch image formed on an image bearing member under a predetermined condition to thereby indirectly estimate the toner density of a developer, etc.
In an image forming apparatus of a type which forms a digital latent image on an image bearing member by the use of a laser scanner or an LED array, the amount of toner consumption per page can be relatively accurately estimated from the total value (video count number) of the number of print pixels in an image information signal per page and therefore, this is also known automatic toner replenishment control means (hereinafter referred to as the “video count ATR) of a type which determines a toner replenishment amount correspondingly to this estimated consumption amount.
This video count ATR does not require a developer toner density detecting portion and therefore has the great advantage that the cost thereof can be reduced. This video count ATR, however, suffers from the problem that the error of the toner replenishment amount is gradually accumulated, and requires some means for correcting this and at present, it is difficult to use it singly.
On the other hand, in case where the developer toner density detecting portion is installed in the developing apparatus, the downsizing of the developing apparatus has been desired. Accordingly, the toner density detecting device by the permeability sensor is often selected and used in an automatic toner replenishment control apparatus because it requires only an installation space for the permeability sensor as the developer toner density detecting portion and is of a construction advantageous for downsizing.
This permeability sensor is installed in a portion of a developer conveying path or the like in the developing apparatus in order that the head portion of the permeability sensor including a coil which is a detecting portion may always contact with the developer. The permeability sensor has a detecting coil, which is constituted by a transmitting winding and a detecting winding. Design is made such that a high frequency transmission output is applied to the transmitting winding which is the transmitting portion of the detecting coil in the head, whereby the inductance of the detecting winding is varied in conformity with a variation in permeability conforming to the density of the developer present around the head, and therefore by measuring a variation in the inductance, it is possible to convert the permeability of the developer present around the head into an electrical output value (a voltage value).
Also, the above-described permeability sensor is generally installed in opposed relationship with a developer conveying member rotated to thereby convey the developer. Accordingly, the voltage output value detected from the permeability of the developer fluctuates with the rotation of the developer conveying member. Consequently, when representing the voltage output value detected from the permeability of the developer, use is generally often made of the average value of the output voltage value from the permeability sensor in one full rotation of the developer conveying member. The control of the amount of toner supply to the developing device is effected in conformity with this average value and a toner density reference value.
Now, the conventional developing apparatus has been of a construction in which a foreign substance intervenes between gears which constitute the drive transmitting means of the developing apparatus, whereby the gears which constitute the drive transmitting means of the developing apparatus are damaged, or in which because of the absence of means for detecting a failure state such as the locking of the bearing portion of the developer conveying member, the failure is difficult to notice. Also in the image forming apparatus, design is not made such that in the case that the failure as described above occurs, whereby the torque of a motor for driving the gear of the developing apparatus becomes great, the greatness of the torque is detected. Therefore, even when failure occurred for example, to the motor itself, it could not be detected early. As described above, design is not made such that the failure state of the developing apparatus is detected and therefore, the failure of the developing apparatus is found in some time after printing has been effected and a bad image or the like has occurred and therefore, it has been delayed for a user to notice the failure.
When any failure as described above occurs, the rotation of the developer conveying member stops and the fluctuation of the output voltage value detected from the permeability sensor becomes null and thus, the permeability sensor continues to output a certain constant value.
When this constant value is greater than an average value (the reference value of the toner density, the permeability sensor continues to output a signal so as to replenish the toner supplying apparatus with the toner. In this case, a great amount of toner is supplied from the toner supplying apparatus into the developer container. Accordingly, when such failure as the damage of the gears constituting the drive transmitting means of the developing apparatus, the locking of the bearing portion of the developer bearing member or the locking of the bearing portion of the developer conveying member occurs, the great amount of toner in the developer container is wasted. Also, when a developing apparatus driving motor which is the drive transmitting means of an image forming apparatus main body goes wrong, if the image forming apparatus resumes its image forming operation after the repair of the motor or the like on the image forming apparatus main body side, the toner density in the developer has become abnormally great, and this has sometimes led to the occurrence of the phenomenon called “fogging” that the toner adheres to a imaged portion to be imaged, the occurrence of a bad image such as the scattering of the toner and in the worst case, the unusability of the developing apparatus.
Also, when the above-mentioned constant value is smaller than the average value (reference value of the toner density), the permeability sensor continues to output a signal so as not to replenish the toner supplying apparatus with the toner at all. In this case, the toner supplying apparatus stops replenishing the developer container with the toner and thus, the toner in the developer container becomes null. Accordingly, when the developing apparatus motor which is the drive transmitting means of the image forming apparatus main body goes wrong, if after the repair of the motor or the like on the image forming apparatus main body side, the image forming apparatus resumes its image forming operation in that state, the toner density in the developer has become abnormally small and therefore, the toner is suddenly supplied from the toner supplying apparatus into the developer container, and this has sometimes led to the occurrence of a bad image such as fogging or the scattering of the toner.